Dissertations / Theses on the topic 'Integrated Bragg Gratings'

In this work, the need for an integrated optical dispersive device is discussed, with particular reference to pulse compression of semiconductor mode-locked laser (MLL) pulses that exhibit temporal chirp and therefore, worse than transform limited behaviour. It is shown that current techniques in fibre and integrated dispersion control do not overlap the dispersion regime presented, making it necessary to design a new integrated device for this purpose. A monolithic chirped Bragg grating is presented with dispersion and bandwidth characteristics coinciding with the previously mentioned regimes. The device, based on a deeply etched tapered waveguide design, may be fabricated fully post-growth, lending it a significant advantage over current grating designs that require the pattern to be written into the core material and the upper cladding layers subsequently overgrown. The deeply etched sidewall grating structures provide the requisite high coupling coefficients, and the ability to induce arbitrary apodisation profiles, while the tapered waveguide design allows the same freedom the grating Bragg condition profile. The coupled-mode analysis for a chirped grating structure is presented and used as a basis for a Transfer Matrix Method (TMM) representation of the device. This simulation tool allows modelling of the arbitrary Bragg condition and apodisation profiles for steady state analysis of passive grating devices, Distributed Feedback (DFB) and Distributed Bragg Reflector (DBR) lasers. The fabrication of low loss passive grating devices and DFB lasers is described with particular attention paid to lithography and reactive ion etching methods. In addition, work is presented on a wet chemical oxidation technique for reduction of sidewall roughness in A1GaAs based waveguides. Deeply etched waveguides were shown to exhibit losses reduced by up to 4dBcm[superscript-1] after application of this procedure. The fabricated passive grating devices exhibit transmission and grating phase profiles closely matching those predicted by the simulations, with control shown over both Bragg condition and coupling coefficient. The DFB lasers, again in agreement with simulation, show unique multi-mode behaviour, closely related to the chirped grating modulation profile. Also presented is a method by which sub-100 [m] tapers for transitions between shallow etched and deep etched waveguides may be fabricated for quasi-adiabatic propagation. These tapers provide a means by which integration may be achieved between optical systems with different mode profiles, these being defined by device properties, for example integration of small radius bends and waveguide gain structures. A simulation tool based on teh TMM is derived and a set of optimised tapers are fabricated, their results matched to the simulations. Low loss, low reflectivity tapers are exhibited with properties in close agreement with teh TMM and Finite Difference Time Doain (FDTD) simulations.

Dans la littérature, les réseaux de Bragg intégrés sur silicium sont relativement simples par rapport à leurs contreparties fibrées. Cependant, la fabrication de réseaux plus élaborés permettrait d’améliorer la capacité de traitement du signal des circuits sur silicium. Cette thèse s’attarde donc aux difficultés encourues lors de la conception, de la fabrication et de la caractérisation de réseaux de Bragg sur silicium ayant une réponse spectrale élaborée. Tout d'abord, afin de caractériser la réponse spectrale complexe des réseaux, l’utilisation de filtrage temporel est proposée afin de supprimer les réflexions parasites. Cela a permis d’utiliser des algorithmes de reconstruction fournissant une caractérisation complète de ces structures. De plus, l’ajout d’un filtrage des hautes fréquences spatiales a permis de réduire considérablement le bruit des mesures. Par la suite, les principales sources de distorsions de la réponse spectrale des réseaux ont été identifiées, soit la rugosité des guides et la variation de leur épaisseur. L’impact de ces phénomènes a été étudié numériquement et analytiquement et, pour la première fois, la longueur de corrélation de ces sources de bruit a été caractérisée expérimentalement sur une longueur suffisante. Finalement, deux techniques permettant de diminuer l’impact de ces phénomènes ont été proposées, ce qui a permis de fabriquer les réseaux de Bragg sur silicium ayant la plus petite largeur de bande publiée à ce jour. Également, nous avons fait les premières démonstrations d’apodisation de réseaux de Bragg utilisant uniquement la phase de ces derniers (c.-à-d. apodisation en phase et par superposition). Contrairement aux techniques déjà proposées, ces dernières ont l'avantage de ne pas introduire de distorsions de l'indice effectif, ils sont plus robuste aux erreurs de fabrication et sont compatibles avec l’apodisation de réseaux à corrugations de très petites amplitudes. Finalement, afin d'augmenter la longueur des réseaux tout en gardant leur dimension compatible avec la taille des puces de silicium, les réseaux ont été courbés en forme de spirale compacte. Pour ce faire, la période des réseaux a été modifiée afin de compenser l'effet de la courbure sur l'indice effectif. Ainsi, nous avons démontré que des réseaux de 2 mm de long pouvaient être intégrés sur une surface de 200 µm x 190 µm sans ajout de dégradation spectrale et, surtout, sans restriction sur la structure du design. Ces résultats sont significatifs, car un contrôle précis de la phase et de l’amplitude des réseaux combinés avec la capacité de fabriquer de réseaux longs sont nécessaire afin de réaliser des filtres optiques intégrés avec des réponses spectrales élaborées. Ainsi, le travail présenté dans cette thèse ouvre la porte à de nouveaux designs à base de réseaux de Bragg.
In the literature, integrated Bragg gratings in Silicon-on-Insulator are relatively simple compared to their fibre Bragg grating counterpart. However, elaborate gratings could improve the signal processing capability of the silicon platform. Thus, this thesis addresses the issues that prevent the design, the fabrication and the characterization of Bragg gratings having elaborate spectral response in the silicon platform. Firstly, in order to precisely characterize Bragg gratings complex spectral response, we proposed to suppress parasitic reflections using temporal filtering. The results obtained with measurement technique, when used with an integral layer peeling algorithm, allowed us to retrieve the amplitude and phase profiles of the grating thus providing a complete characterization of the structure. Moreover, the addition of a low-pass spatial filter allowed improving the characterization process by reducing the measurement noise. Secondly, the main sources of distortion of Bragg gratings spectral response have been identified to be the sidewall roughness and the wafer height fluctuation. An exhaustive study of the impact of these phenomena has been done both numerically and analytically. Furthermore, for the first time, the autocorrelation of these noise sources has been characterized experimentally on a sufficient length. Finally, improvements in the waveguide designs have reduced significantly these effects which allowed the fabrication of Bragg gratings in silicon with the smallest bandwidth published to date. Thirdly, the first demonstration of apodized Bragg gratings using only phase modulation of the structure has been done (i.e. phase apodisation and superposition apodisation). Unlike already published techniques, the later ones have the advantage to be robust to deep-UV lithography and fabrication errors. Furthermore, they do no introduce distortions into the grating phase profile and they are compatible with gratings having small recesses. Finally, in order to increase the grating length while keeping their dimension compatible with the silicon chip size, we proposed to bend them in a compact spiral shape. To do this properly, the curvature impact on the effective index has been modeled and compensated successfully by modifying the grating period. Thus, we have shown that 2 mm long gratings can be integrated on a surface of 200 µm x 190 µm without the addition of spectral degradation and without restrictions on the design structure. These results are of importance because longer grating structures with weaker coupling coefficients and a precise control both on its phase and amplitude are required in order to achieve integrated optical filters with elaborate spectral responses. Thus, we believe that the work presented in this thesis open the door to many new grating-based optical filter designs compatible with integrated optics technologies.

Dans la littérature, les réseaux de Bragg intégrés sur silicium sont relativement simples par rapport à leurs contreparties fibrées. Cependant, la fabrication de réseaux plus élaborés permettrait d’améliorer la capacité de traitement du signal des circuits sur silicium. Cette thèse s’attarde donc aux difficultés encourues lors de la conception, de la fabrication et de la caractérisation de réseaux de Bragg sur silicium ayant une réponse spectrale élaborée. Tout d'abord, afin de caractériser la réponse spectrale complexe des réseaux, l’utilisation de filtrage temporel est proposée afin de supprimer les réflexions parasites. Cela a permis d’utiliser des algorithmes de reconstruction fournissant une caractérisation complète de ces structures. De plus, l’ajout d’un filtrage des hautes fréquences spatiales a permis de réduire considérablement le bruit des mesures. Par la suite, les principales sources de distorsions de la réponse spectrale des réseaux ont été identifiées, soit la rugosité des guides et la variation de leur épaisseur. L’impact de ces phénomènes a été étudié numériquement et analytiquement et, pour la première fois, la longueur de corrélation de ces sources de bruit a été caractérisée expérimentalement sur une longueur suffisante. Finalement, deux techniques permettant de diminuer l’impact de ces phénomènes ont été proposées, ce qui a permis de fabriquer les réseaux de Bragg sur silicium ayant la plus petite largeur de bande publiée à ce jour. Également, nous avons fait les premières démonstrations d’apodisation de réseaux de Bragg utilisant uniquement la phase de ces derniers (c.-à-d. apodisation en phase et par superposition). Contrairement aux techniques déjà proposées, ces dernières ont l'avantage de ne pas introduire de distorsions de l'indice effectif, ils sont plus robuste aux erreurs de fabrication et sont compatibles avec l’apodisation de réseaux à corrugations de très petites amplitudes. Finalement, afin d'augmenter la longueur des réseaux tout en gardant leur dimension compatible avec la taille des puces de silicium, les réseaux ont été courbés en forme de spirale compacte. Pour ce faire, la période des réseaux a été modifiée afin de compenser l'effet de la courbure sur l'indice effectif. Ainsi, nous avons démontré que des réseaux de 2 mm de long pouvaient être intégrés sur une surface de 200 µm x 190 µm sans ajout de dégradation spectrale et, surtout, sans restriction sur la structure du design. Ces résultats sont significatifs, car un contrôle précis de la phase et de l’amplitude des réseaux combinés avec la capacité de fabriquer de réseaux longs sont nécessaire afin de réaliser des filtres optiques intégrés avec des réponses spectrales élaborées. Ainsi, le travail présenté dans cette thèse ouvre la porte à de nouveaux designs à base de réseaux de Bragg.
In the literature, integrated Bragg gratings in Silicon-on-Insulator are relatively simple compared to their fibre Bragg grating counterpart. However, elaborate gratings could improve the signal processing capability of the silicon platform. Thus, this thesis addresses the issues that prevent the design, the fabrication and the characterization of Bragg gratings having elaborate spectral response in the silicon platform. Firstly, in order to precisely characterize Bragg gratings complex spectral response, we proposed to suppress parasitic reflections using temporal filtering. The results obtained with measurement technique, when used with an integral layer peeling algorithm, allowed us to retrieve the amplitude and phase profiles of the grating thus providing a complete characterization of the structure. Moreover, the addition of a low-pass spatial filter allowed improving the characterization process by reducing the measurement noise. Secondly, the main sources of distortion of Bragg gratings spectral response have been identified to be the sidewall roughness and the wafer height fluctuation. An exhaustive study of the impact of these phenomena has been done both numerically and analytically. Furthermore, for the first time, the autocorrelation of these noise sources has been characterized experimentally on a sufficient length. Finally, improvements in the waveguide designs have reduced significantly these effects which allowed the fabrication of Bragg gratings in silicon with the smallest bandwidth published to date. Thirdly, the first demonstration of apodized Bragg gratings using only phase modulation of the structure has been done (i.e. phase apodisation and superposition apodisation). Unlike already published techniques, the later ones have the advantage to be robust to deep-UV lithography and fabrication errors. Furthermore, they do no introduce distortions into the grating phase profile and they are compatible with gratings having small recesses. Finally, in order to increase the grating length while keeping their dimension compatible with the silicon chip size, we proposed to bend them in a compact spiral shape. To do this properly, the curvature impact on the effective index has been modeled and compensated successfully by modifying the grating period. Thus, we have shown that 2 mm long gratings can be integrated on a surface of 200 µm x 190 µm without the addition of spectral degradation and without restrictions on the design structure. These results are of importance because longer grating structures with weaker coupling coefficients and a precise control both on its phase and amplitude are required in order to achieve integrated optical filters with elaborate spectral responses. Thus, we believe that the work presented in this thesis open the door to many new grating-based optical filter designs compatible with integrated optics technologies.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2002.
Includes bibliographical references (p. [207]-213).
This thesis provides an in-depth study of optical filters made using integrated Bragg gratings and Bragg resonators. Various topologies for making add/drop filters using integrated gratings are outlined. Each class of devices is studied in detail and the theoretical tools needed for designing the add/drop are developed. First-order filters using Bragg resonators do not meet WDM add/drop filter specifications. Consequently, schemes to design higher-order filters are derived. The relative advantages and disadvantages of the various possiblities are outlined. Preliminary integrated Bragg grating devices, in InP, were designed using the tools developed. The fabricated devices were measured. The measurements revealed low-loss structures with a < 0.1 cm-l and high-Q Bragg resonators with Q > 40, 000. Measurements on higher-order inline coupled Bragg resonator filters showed flat-top and fast roll-offs. The results of the measurements and comparison with the theory are presented for the various devices. The results reveal that Bragg grating based devices offer tremendous potential for use as add/drop filters in WDM systems.
by Mohammad Jalal Khan.
Ph.D.

Silicon-on-insulator (SOI) is rapidly emerging as a very promising material platform for integrated photonics. As it combines the potential for optoelectronic integration with the low-cost and large volume manufacturing capabilities and they are already accumulate a huge amount of applications in areas like sensing, quantum optics, optical telecommunications and metrology. One of the main limitations of current technology is that waveguide propagation losses are still much higher than in standard glass-based platform because of many reasons such as bends, surface roughness and the very strong optical confinement provided by SOI. Such high loss prevents the fabrication of efficient optical resonators and complex devices severely limiting the current potential of the SOI platform. The project in the first part deals with the simple waveguides loss problem and trying to link that with the polarization problem and the loss based on Fabry-Perot Technique. The second part of the thesis deals with the Bragg Grating characterization from again the point of view of the polarization effect which leads to a better stop-band use filters. To a better comprehension a brief review on the basics of the SOI and the integrated Bragg grating ends up with the fabrication techniques and some of its applications will be presented in both parts, until the end of both the third and the fourth chapters to some results which hopefully make its precedent explanations easier to deal with.

SWIFTS (pour Stationary-Wave Integrated Fourier-Transform Spectrometer) est un concept de spectromètre s'appuyant sur l'optique intégrée pour proposer un système de mesure compact et de très haute résolution. Il combine une technique d'interférométrie développée par Gabriel Lippmann avec des technologies de microélectroniques actuelles. La technologie SWIFTS sera ici utilisée en tant qu'interrogateur de fibre de Bragg. En effet, combiner ce spectromètre avec des fibres de Bragg très sensibles, telle qu'une cavité Fabry-Perot à réseaux de Bragg (GFPC) d'une longueur de 20 mm, permettra de mesurer des variations de température et de déformation très précises. Les applications des fibres de Bragg sont nombreuses, particulièrement dans la surveillance de structure de génie civil ou dans la sureté nucléaire avec des précisions de l'ordre du microstrain. Cependant, les capteurs par fibres de Bragg n'ont jamais atteint la sensibilité nécessaire aux observations en science de la terre. Une précision de quelques dizaines de nanostrain serait pourtant d'un intérêt majeur dans l'étude des processus volcaniques et sismologiques. Je présente dans cette thèse la première utilisation d'un tel spectromètre de Fourier associé à des capteurs de Bragg pour mesurer des déformations dans différentes gammes allant du millistrain au nanostrain. Dans un premier temps, des déformations sur une petite structure en béton armé amenée jusqu'à l'état limite de fissuration permettront de qualifier différents capteurs à fibres de Bragg dans leur milieu d'usage. Dans un deuxième temps, des mesures de déformations liées au phénomène de la marrée terrestre sont proposées. Ces mesures, effectuées au Laboratoire Souterrain à Bas Bruit (LSBB) de Rustrel, donnent des précisions de l'ordre de 30 nanostrains sur une courte base et ouvrent la voie à d'autres mesures de phénomènes géophysiques pour cet instrument
SWIFTS, or Stationary-Wave Integrated Fourier-Transform Spectrometer, is an extremely integrated very high resolution spectrometer. This spectroscopy technology represents a major advance in the field and will be used here as a Fiber Bragg Gratings interrogator. Combining such a spectrometer with very sensitive Bragg sensors, like grating Fabry-Perot cavity (GFPC) as long as 20 mm, will allow to measure high precision temperature or strain variation. Applications of Bragg sensors are numerous, especially in structure monitoring and nuclear power plants safety. Despite promising capabilities, Bragg sensors never reached the desired sensibility for earth-science observation purposes. Present applications are restricted to civil-engineering strain-gauge sensors with microstrain sensitivity. However, the ability to detect and record signals of the order of a few tens of nanostrain is of great interest to monitor and model the volcanic and seismological processes. I demonstrate in this thesis the first use of a Fourier-Transform spectrometer combined with Fiber Bragg Sensors in a field configuration to achieve extremely high precision measurement on earth's crustal deformation. Precisions of thirty nanostrains on a very short base were achieved in the Low-Noise Underground Laboratory (LSBB) at Rustrel. Crustal monitoring opens the way for numerous applications especially in geophysics. A second study presented in this thesis aims at benchmarking several strain sensors based on optical fiber Bragg grating. For this purpose, two reinforced concrete beams have been tested in three points bending up to ultimate limit state

The main objectives of this thesis were to develop a lowtemperature PECVD process suitable for optoelectronicintegration, and to optimize silica glass composition forUV-induced modifications of a refractive index in PECVDfabricated planar devices. The most important achievement isthe successful development of a low temperature silicadeposition, which for the first time makes it is possible tofabricate good quality low loss integrated components whilekeeping the temperature below 250oC during the entirefabrication process. Two strong absorption peaks thatappear at1.5 mm communication window due to N-H and Si-H bonds have beencompletely eliminated by process optimization. This openspossibilities for monolithic integration with other,temperature sensitive devices, such as semiconductor lasers anddetectors, or polymer-based structures on the common siliconplatform. PECVD technology for low loss amorphous silicon inapplication to SiO2/Si based photonic crystal structures hasbeen also optimized to remove hydrogen incorporated during thedeposition process, responsible for the porosity of thedeposited material and creation of similar to silica absorptionbands.

Change of the refractive index of germanium doped silicaunder UV irradiation is commonly used for fabrication of UVinduced fiber Bragg gratings. Here we describe our achievementsin fabrication of fiber Bragg gratings and their application todistributed sensor systems. Recently we have built up a laserlab for UV treatment in application to planar technology. Wehave demonstrated the high photosensitivity of PECVD depositedGe-doped glasses (not thermally annealed) even without hydrogenloading, leading to a record transmission suppression of 47dBin a Bragg grating photoinduced in a straight buried channelwaveguide. We have also used a UV induced refractive indexchange to introduce other device modifications or functions,such as phase shift, wavelength trimming and control ofpolarization birefringence.The developed low temperature technology and the UVprocessing form a unique technology platform for development ofnovel integrated functional devices for optical communicationsystems.

A substantial part of the thesis has been devoted tostudying different plasma deposition parameters and theirinfluence on the optical characteristics of fabricatedwaveguides to find the processing window giving the besttrade-off between the deposition rate,chamber temperatureduring the process, optical losses and presence of absorptionbands within the interesting wavelength range. The optimalconditions identified in this study are low pressure (300-400mTorr), high dilution of silane in nitrous oxide and high totalflow (2000 sccm), low frequency (380 KHz) RF source and high RFpower levels (800-1000 W).

The thesis provides better understanding of the plasmareactions during the deposition process. RF Power is the keyparameter for increasing the rate of surface processes so as toaccommodate each atomic layer in the lowest energy statepossible. All the process conditions which favor a moreenergetic ion bombardment (i.e. low pressure, low frequency andhigh power) improve the quality of the material, making it moredense and similar to thermal oxide, but after a certain pointthe positive trend with increasing power saturates. As theenergy of the incoming ion increases, a competing effect setsin at the surface: ion induced damage and resputtering.

Finally, the developed technologies were applied for thefabrication of some test and new concept devices for opticalcommunication systems including multimode interference (MMI)-based couplers/splitters, state-of-the-art arrayed waveguidegrating-based multi/ demultiplexers, the first Bragg gratingassisted MMI-based add-drop multiplexer, as well as moreresearch oriented devices such as a Mach-Zehnder switch basedon silica poling and a Photonic Crystal-based coupler.

Keywords:silica-on-silicon technology, PECVD, plasmadeposition, photonic integrated circuits, planar waveguidedevices, UV Bragg gratings, photosensitivity, arrayed waveguidegratings, multimode interference couplers, add-dropmultiplexers.

This thesis reports the development and modification of direct ultraviolet (UV) written planar integrated optical Bragg grating refractometers for detection of gases and vapours. The technique of direct UV writing utilises the localised refractive index increase within a UV-photosensitive silica layer, when the layer is exposed to a tightly focussed UV beam, to fabricate a wide range of optical waveguides and optical components. One such component, the Bragg grating, is used as an optical sensor for changes in refractive index. This thesis reports on the development of practical planar integrated optical Bragg grating gas sensors. This has been achieved through the use of two approaches. The first approach was to increase the number of gas molecules that can interact with the evanescent wave through the use of films of material that extended normally to the surface of the sensor device. Upon functionalisation of a planar Bragg grating sensor device with sol-gel thin films, a response between relative humidity and Bragg wavelength shift was revealed. Functionalisation of the Bragg grating sensor device with a polysiloxane polymer imparted sensitivity to solvent vapours. A quantitative structure-activity relationship (QSAR) approach was used to develop a linear regression model, between Bragg wavelength shift and solvent properties, which had good predicting power. The second approach was to utilise the associated change in refractive index of a material, when the material changed colour upon exposure to a gas, to create a measurable Bragg wavelength shift. This method was successfully achieved upon interrogation of a Bragg grating sensor device, which had been modified with an encapsulated pH sensitive organic dye upon exposure to hydrogen chloride fumes.

This dissertation presents the fabrication and analysis of in-fiber devices based on elliptical core D-shaped optical fiber. Devices created inside optical fibers are attractive for a variety of reasons including low loss, high efficiency, self-alignment, light weight, multiplexibility, and resistance to electromagnetic interference. This work details how D-fiber can be used as a platform for a variety of devices and describes the creation and performance of two of these devices: an in-fiber polymer waveguide and a surface relief fiber Bragg grating. In D-fiber the core is very close to the flat side of the ‘D’ shape. This proximity allows access to the fields in the fiber core by removal of the cladding above the core. The D-fiber we use also has an elliptical core, allowing for the creation of polarimetric devices. This work describes two different etch processes using hydrofluoric acid (HF) to remove the fiber cladding and core. For the creation of devices in the fiber core, the core is partially removed and replaced with another material possessing the required optical properties. For devices which interact with the evanescent field, cladding removal is terminated before acid breaches the core. Etching fibers prepares them for use in the creation of in-fiber devices. Materials are placed into the groove left when the core of a fiber is partially removed to form a hybrid waveguide in which light is guided by both the leftover core and the inserted material. These in-fiber polymer waveguides have insertion loss less than 2 dB and can potentially be the basis for a number of electro-optic devices or sensors. A polarimetric temperature sensor demonstrates the feasibility of the core replacement method. This work also describes the creation of a surface relief fiber Bragg gratings (SR-FBGs) in the cladding above the core of the fiber. Because it is etched into the surface topography of the fiber, a SR-FBG can operate at much higher temperatures than a standard FBG, up to at least 1100 degrees Celsius. The performance of a SR-FBG is demonstrated in temperature sensing at high temperatures, and as a strain sensor.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.
Includes bibliographical references (p. 237-247).
by Thomas E. Murphy.
Ph.D.

This thesis presents theoretical and experimental studies of planar Bragg grating devices for all-optical signal processing. Bragg gratings offer a route to realise many systems for all-optical signal processing including photonic Hilbert transformers. The fabrication of Bragg gratings in a planar format allows monolithic integration with traditional planar components and micro-heaters to realise devices with desired performance. Photonic Hilbert transformers offer potential for a wide range of applications such as single-sideband modulation, and also provide operational bandwidths and speeds far beyond current electronic technologies. A series of experimental demonstrations of photonic Hilbert transformers based on apodised planar Bragg gratings with phase-shifts are presented. Devices implementing fractional order Hilbert transform are also investigated. Grating structures are synthesised to achieve improved spectral quality including the demonstration of devices with Terahertz bandwidths. A direct UV grating writing technique based on phase-controlled interferometry is proposed and demonstrated to fabricate arbitrary Bragg gratings in a silica-on-silicon platform. Electro-optic phase modulation of one beam in the interferometer is used to manipulate the fringe pattern and control the parameters of Bragg gratings and waveguides. Along with the unique micron-order writing spot, modulation linearity and translation consistency ensures the desired grating apodisation profile is achieved. Furthermore, the significant improvement in fringe control results in larger grating index contrast, enabling Terahertz bandwidth devices. Finally, the system utilising the phase controlled UV writing technique is applied to the inscription of fibre Bragg gratings. Various kinds of fibres are experimentally tested in the work. The small writing spot shows potential and significant capability to inscribe arbitrary Bragg gratings into fibre structures.

This thesis presents experimental and theoretical work towards the development of advanced integrated planar optical devices for wavelength division multiplexing (WDM) applications in optical communication systems. The presented work lies within a broad range of research areas, namely: design and simulation of novel Bragg grating based WDM passive devices, their performance characterization in simulated optical communication systems, fabrication and characterization of photosensitive thin films and finally device fabrication using ultraviolet induced refractive index changes. A complete model for the analysis of Bragg grating assisted devices in waveguide structures has been developed. Bragg grating based optical Add/Drop multiplexers (OADM) have been simulated and studied by using this modelling tool. A fully optimised design for an OADM based on null coupler and tilted Bragg grating has been proposed. This device can exhibit optimised Add and Drop actions with suppressed backreflections and crosstalk to a level lower than -40 dB. A novel interferometric OADM configuration based on a full cycle full (100%) coupler is also proposed. This design exhibits fully optimised and symmetrical Add/Drop actions in contrast to the compromised performance of traditional interferometric configurations. A software simulation tool has also been developed and employed for the theoretical characterization of optical filters, linking this way the proposed devices to real communication system issues related to high bit rate WDM networks. The effect of group delay ripple in WDM filters is studied for different modulation formats and a simplified figure of merit is proposed for the characterization of the effect. For the fabrication of photosensitive thin film structures, a prototype in-house Flame Hydrolysis Deposition facility was built and it was initially characterized. Further experimental work involved detailed analysis and characterization of highly photosensitive Lead Germanate glasses grown by Pulsed Laser Deposition. A developed direct UV-writing facility is presented and major issues around the functionality of the technique are discussed, by demonstrating solutions for the control of the optical system. A rapid heat treatment technique is also proposed for locking the enhanced photosensitivity in deuterium loaded germanosilicate glasses and successful preliminary results are demonstrated. This method should allow finally the fabrication of complex all-UV-written devices, which has been limited to date by the degrading photosensitivity during UV writing, due to rapid deuterium outdiffusion.

Ces trois années de thèse balayent la conception, la fabrication et la caractérisation de lasers III V sur silicium à 1.31 µm pour les data-communications. Le design des sources englobe notamment l’optimisation du couplage entre l’empilement III V et le silicium, effectué grâce à un taper adiabatique, ainsi que l’étude de la cavité laser inscrite, comme le taper, dans le silicium. Trois types de cavités à base de réseaux ont été étudiées: les cavités à contre-réaction distribuée (DFB pour distributed feedback), celles à réseaux de Bragg distribuées (DBR pour distributed Bragg reflector) et enfin celles à réseaux de Bragg échantillonnées (SGDBR pour sampled-grating DBR). Deux solutions ont été abordées concernant les lasers DFB: le réseau, inscrit dans le guide silicium sous la zone de gain, est soit gravé au-dessus du guide Si, soit sur les côtés. La seconde possibilité, appelée ‘DFB lasers couplés latéralement’, simplifie la fabrication et élargit les possibilités de design.Les lasers DFB fabriqués sont très prometteurs en terme de puissance (avec jusque 20 mW dans le guide) ainsi que pour leur pureté spectrale (avec une différence de plus de 50 dB entre le mode principal et le mode suivant). Une accordabilité spectrale de plus de 27 nm a été obtenue en continu avec les lasers SGDBR tout en conservant une très bonne pureté spectrale et une puissance de plus de 7 mW dans le guide
This 3 years work covers the design, the process and the characterization of III-V on silicon lasers at 1.31 µm for datacommunication applications. In particular, the design part includes the optimization of the coupling between III V and Si using adiabatic tapers as well as the laser cavity, which is formed within the Si. Three types of lasers were studied, all of them based on cavities which consist of gratings: distributed feedback (DFB) lasers, distributed Bragg reflector (DBR) lasers and finally sampled-grating DBR (SGDBR) lasers. Regarding the DFB lasers, two solutions have been chosen: the grating is either etched on top or on the edges of the Si waveguide to form so called vertically or laterally coupled DFB lasers. The latter type, quite uncommon among hybrid III V on Si technologies, simplifies the process fabrication and broadens the designs possibilities.Not only the lasers demonstrated show high output powers (~20 mW in the waveguides) but also very good spectral purities (with a side mode suppression ratio higher than 50 dB), especially for the DFB ones. The SGDBR devices turn out to be continuously tunable over a wavelength range higher than 27 nm with a good spectral purity as well and an output power higher than 7 mW in the waveguide with great opportunities of improvement

This thesis presents a simulation and experimental study of a true time-delay (TTD) beamforming network using a Bragg grating prism on Ge-doped silica-on-silicon planar integrated optical waveguide for application in phased array antennas (PAA). The Bragg grating prism is designed and fabricated on planar optical waveguides and the true time-delay beamforming module is implemented using the fabricated waveguide Bragg grating prism and other photonic components. When dealing with a remotely controlled PAA, the dispersive properties of a standard single mode fiber must be taken under consideration. To this effect, a simulation study has been carried out and is detailed in this thesis. The Bragg grating prism used in the beamformer is composed of chirped gratings of different lengths but of same total chirp in order to produce a true time-delay progression. Two modulation techniques are considered, single sideband (SSB) and double sideband (DSB) modulation. SSB modulation is shown to be well suited for broadband operations with little impact on the orientation of the mainlobe resulting from chromatic dispersion. (Abstract shortened by UMI.)

In this thesis, miniaturized wavelength interrogators based on planar lightwave circuits (PLCs) are investigated and developed for the optical fiber sensing applications in the aircraft structural health monitoring (SHM) and optofluidic analysis. Two interrogation systems based on an arrayed waveguide grating (AWG) and an Echelle diffractive grating (EDG) are developed and used to convert the optical sensing signals into strain, temperature, vibration, damage, and humidity information for the aircraft SHM. A fiber Bragg grating (FBG) sensing system using developed interrogators is then demonstrated in a field test for aircraft SHM applications. For optofluidic analysis, a PLCs based optofluidic device consisting of two on-chip lens sets is built to enhance the optical manipulation capability of particles. Then, a solution to a multi-functional Lab-on-a-Chip platform for optofluidic analysis is proposed, which integrates the developed particle maneuvering device, grating-structured sensors, and miniaturized interrogators.

Nanophotonic circuits for single photon emitters. The work demonstrated in this thesis is dedicated to the engineering, simulation, fabrica-tion and investigation of the essential element base to develop hybrid fully integrated nanopho-tonic circuit with coupled single photon emitter on chip. Combining several individually opti-mized stages of photonic devices, interconnected by nanoscale waveguides on chip with eva-nescently coupled single photon emitter, is a key step to the realization of such a scheme. The main requirements which should be satisfied for building such a hybrid system on-chip, and are thus the subject of this Thesis, are, namely: integration of single photon photostable source with high Quantum Yield (QY) on chip, efficient coupling of the emitted light to nanophotonic cir-cuits, and efficient filtering of the excitation light. Silicon nitride-on-insulator was used in all the projects described in this Thesis as the platform for the realization of photonic circuits. It provides low-loss broadband optical transparency covering the entire visible range up to the near infrared spectrum. Furthermore, sufficiently high refractive index contrast of Si3N4 on SiO2 enables tight confinement of the mode in the waveguide structure and the realization of photonic circuits with small footprint. A drastic increase of the coupling efficiency of the emitted light into the waveguide mode can be achieved by placing single-photon emitter on photonic crystal cavity because of its high Quality factor and small mode volume enabling a high Purcell enhancement. To this end, a novel cross-bar 1D freestanding photonic crystal (PhC) cavity was developed for evanescent integration of single photon emitter, in particular Nanodiamonds (NDs), onto the region of the cavity. The novelty of this photonic structure is that collection of emitted light is provided via waveguide, which consists of PhC, whereas direct optical excitation is obtained through a crossed waveguide in the orthogonal direction of the in-plane cavity. Optimization of the PhC cavity architecture was performed via rounds of simulations and ver-ified by experimental measurements of fabricated devices on chip, which were found in excel-lent agreement. The next round of simulations was performed to define an optimal position of the source in the cavity region to achieve maximum Purcell enhancement, which was realized via Local Density of States (LDOS) computation. Thus, placing a single photon emitter into a determined position on the cavity region of the developed cross-bar 1D freestanding PhC enables an increase in the transmission coupling efficiency into cavity up to =71% in comparison with computed 41% in the case of coupling into waveguide mode of cross-bar structure without PhC. To block the pump light and at the same time transmit the fluorescent emitted light, compact and low-loss cascaded Mach–Zehnder interferometers (MZIs) tunable filters in the visible region embedded within nanophotonic circuit, were realized. Tunability was provided via thermo-optic effect. The design of this device, namely geometry and shape of the microheater, was optimized via thermo-optic measurements, to achieve low electrical power consumption (switching power of 12.2 mW for the case of a spiral-shape microheater), high filtration depth and low optical insertion loss. The novel design with double microheaters on top of both arms of single and cascaded MZIs allows doubling the range of the shifting amplitude of the interference fringes. The demonstrated architecture of tunable filter is multifunctional, namely allowing transmission and filtering of the desired wavelengths in a wide wavelength range. In particular, filtration depth beyond 36.5 dB of light with 532 nm wavelength and simultaneous transmission of light with 738 nm wavelength, which correspond respectively to excitation and emission wavelength of the silicon-vacancy color center in diamond, was demonstrated. The results were published in Ovvyan, A. P.; Gruhler, N.; Ferrari, S.; Pernice, W. H. P. Cascaded Mach-Zehnder interferometer tunable filters. Journal of Optics 2016, 18, 064011 https://doi.org/10.1088/2040-8978/18/6/064011 Another filter with non-repetitive stopband with bandwidth of several nanometers was developed in this thesis. A non-uniform Bragg grating filter with novel double Gaussian apodization was proposed, whose fabrication required a single lithography step. This optimized Bragg filter provides a 21 dB filtration depth with a 3-dB bandwidth of 5.6 nm, insuring negligible insertion loss in the best case, while averaged insertion loss in reflected signal is 4.1dB (including loss in splitter). One of the first Hybrid organic molecule Dibenzoterrylene (DBT) coupled on chip to a nanophotonic circuit was demonstrated in this thesis. DBT is a photostable single photon source in the near infrared spectrum at room and at cryogenic temperature, with almost unitary quan-tum yield. In order to protect the molecule against oxidization DBT was embedded in a host matrix – thin Anthracene crystal (DBT:Ac), which increases photostability. Mirror enhanced grating couplers were employed as convenient output ports for ridge Si3N4 waveguide to detect single photons emitted from integrated Dibenzoterrylene (DBT) molecules at room temperature. The coupling ports were designed for waveguide structures on transparent silica substrates for light extraction from the chip backside. These grating ports were employed to read out optical signal from waveguides designed for single-mode operation at λ=785 nm. DBT molecule was coupled evanescently to the waveguide, and upon excitation of isolated single molecule, emitted single photon signal was carried inside the waveguide to the outcou-pling regions. Using a Hanbury Brown and Twiss setup pronounced antibunching dip was read out from a single molecule via the grating couplers, which confirms the quantum nature of the outcoupled fluorescent light. Simulated and measured transmission coupling efficiency of sin-gle photon emission into the waveguide mode equals =42%. The results were published in P. Lombardi*, A. P. Ovvyan*, S. Pazzagli, G. Mazzamuto, G. Kewes, O. Neitzke, N. Gruhler, O. Benson, W. H. P. Pernice, F. S. Cataliotti, and C. Toninelli. Photostable Molecules on Chip: Integrated Sources of Nonclassical Light. ACS Photonics 2018, 5, 126−132, DOI: 10.1021/acsphotonics.7b00521. * P. Lombardi and A. P. Ovvyan contributed equally to this work. Engineered nanophotonic elements integrated in optical circuits with coupled single photon emitter on chip allow simultaneously to enhance the emitted light by coupling it into resonant PhC cavity modes, to spatially separate the excitation light from the enhanced single photon emission and to filter out pump light. Enhancement of the emission rate leads to a sig-nificant increase of the coupling efficiency into cavity. Beforehand performed simulations were an essential step in order to design, build and optimize the architecture of the nanophotonic devices. Local Density of States enhancement computation was especially necessary to pre-cisely determine optimized position of the source on PhC cavity region to obtain maximum enhancement of the emission rate. To evaluate transmission coupling efficiency of emitted light into the cavity (β-factor), an extra round of simulations was performed. The integrated photonic elements investigated and optimized in this Thesis, will be further employed for the realization of hybrid photonic circuits with integrated single photon sources: silicon-vacancy, nitrogen-vacancy centers in diamond as well as single organic molecule and semiconducting single-walled carbon nanotubes.